1. Field of the Invention
The present invention relates to an anti-curl agent, an ink jet ink containing the anti-curl agent, a method for ink jet recording to form images by ejecting the ink, and a method for reducing curl of the recording medium using the ink.
2. Related Background Art
Ink jet recording method ejects ink droplets directly onto a water-absorptive medium like paper, to which the ink is attached to form images thereon. Because the ink-jet printer is compact and low cost, it is widely used as the output machine of the personal computers at home and offices. Moreover, an ink jet recording method is suitably applicable for recording an image with high resolution and quality at a high speed.
The ink for this type of recording method generally comprises water as a major component, a colorant, and a polar solvent such as glycerin to prevent ink deposition to the fine nozzles. Such an ink has advantages of being odorless and having a high flash point. However, when a large quantity of the ink is applied to a recording medium to form an image with the colorant in the ink, a large quantity of water may be absorbed by the recording medium because the component of the ink is mostly water. As a result, the printing speed sometimes depends on the penetration speed of the ink into the recording medium.
On the other hand, when plain paper is used as a recording medium, the shape may change after absorbing a large quantity of water. There are two general categories in these changes; one is cockling and the other curl. The curl phenomenon means shift of the paper edge towards the center of the printed side or the backside. Curl to the backside is referred to as reverse curl. Curl may occur immediately after printing or may appear with a lapse of time. Eventually the paper may become cylindrical in an extreme case, and storage of the recording media becomes very inconvenient.
Some attempts have been made to solve these problems. For example, Japanese Unexamined Patent Publication No. H06-240189 discloses a technique to reduce the curl phenomenon by adding 4 to 20% by mass of sugar to the ink.
Japanese Unexamined Patent Publication No. H06-157955 discloses the compounds having multiple hydroxyl groups as the anti-curl agent. These compounds include diols of 3 to 11 carbon atoms and ethylene oxide or polyoxyalkylene derivatives thereof, ethylene oxide or polyoxyalkylene derivatives of glycerin, pyranosides and derivatives thereof, and polyoxyalkylene derivatives of aliphatic polyamine.
Japanese Unexamined Patent Publication No. H09-176538 discloses an anti-curl agent of a carboxylic acid amide, e.g., acetamide, propionamide, isobutylamide or hexanamide; alkylurea of up to 6 carbon atoms, e.g., butylurea, 1,3-dimethylurea, ethylurea, propylurea or 1,3-diethylurea; or nitrogen-containing cyclic compound, e.g., tetrahydropyrimidone or imidazolidinone, to be incorporated in an ink at least 10% by mass or more.